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Blowby Here

Updated on December 9, 2013

What Is Blowby?

Blowby is the result of wear in a gas or diesel engine.

Blowby inhibits the performance of the car, truck, pump, ATV, motorcycle or whatever machine the engine powers.

When an Engine is New...

The rings and cylinders are designed to match each other. Using the oil from below in the crankcase, the rings create a seal that keeps the oil out of the combustion chamber and the expanding combustion gases from blowing by the ring into the crankcase. The combustion energy is fully used to push the piston downward, driving the crankshaft and ultimately turning the wheels. New cars have more power and better fuel economy.

New Car Engine

New car engine
New car engine | Source

Worn From Circular to Oval

The ring is actually a spring that presses against the cylinder wall. Viewed from the top, the new cylinder is round, as is the ring. As the piston moves up and down, a properly functioning ring actually rotates around the piston in its groove, reducing uneven wear. As long as the cylinder is cylindrical (round as seen from the top), and the ring is rotating, the ring does its job and seals the oil below and the energy above.

During normal operation, both the cylinder and the ring begin to wear. The cylinder wears the most on opposite sides, 90 degrees off the wrist pin. This creates an oval shape to the cylinder. Ovality of the cylinder is one of the primary causes of blowby because the ring can no longer seal that worn area. Combustion gases are blown by the ring into the crankcase, hence the name blowby. This is seen as reduced compression as measured by a compression test. Ring and cylinder wear are not the only causes of compression loss. When valves are worn, they will also allow combustion gasses to escape. Mechanics have specific tests they can perform to determine if compression loss is caused by ring or valve wear.

Stuck Rings

Blowby is also caused by stuck rings. As mentioned above, the ring is designed to rotate around the piston in its groove. However, carbon deposits are often left behind in the combustion process. Complex fuel molecules simply do not burn completely and are often left behind as a black deposit. A common complex fuel molecule is the asphaltine molecule. I like to use this example because even the casual reader can easily visualize the black tarry substance that must be left behind on the surfaces inside the engine. Not even Chevron’s detergent, Techron fully cleans up carbon deposits.

These deposits typically accumulate on the upper surface of the top ring of the piston. As these deposits accumulate, the ring movement becomes restricted, eventually resulting in the ring actually getting stuck. The deposits block the top surface and even wedge between the ring and its groove. When the ring sticks, the ring seals poorly and actually accelerates wear.

Look Out for Oil

Blowby can be seen by the casual mechanic (car owner) without having to pay for a compression test by removing the oil filler cap while the engine is running. Be careful – if the engine is hot, the oil is too and can burn you. Do this test when the engine is cool. In moderate to severe cases of blowby, the oil actually spits out the oil filler opening. When you see this, turn off the engine or put the cap back on or you will have a big mess to clean up.

Even if the blowby is not enough to create visible “oil spit” the pulsating air can be detected at the oil filler cap. Hey – if the engine is hot, don’t just put your hand on the hot oil filler cap and burn yourself. Be careful. Many engines have a dual position release to the filler cap so that by turning part way, the cap is loose but will not lift off. This is a valuable feature to use. If the cap bounces in this position, the blowby pressure is the cause. Tighten the cap before closing the hood.

Blowby is also detected in older engines and diesel engines as oil dripping from the breather tube of the engine. As the combustion gases are injected into the crankcases of older and many diesel engines with breather tubes, the pressure splashes the oil (remember “oil spit”) into the opening of the breather tube. There is much to say about emission control and why the newer engines do not have breather tubes, but that is for another discussion. Nevertheless, the result is oil on the pavement under where the vehicle is parked. This is not to be confused with leaking oil gaskets, but the result is the same, a puddle or oil spot under the vehicle.

Excess oil usage or burning oil is another clear sign of cylinder/ring wear. This is probably the most common sign and although it is not blowby in the sense of combustion gases blowing into the crankcase, it is the opposite. The oil leaks past the ring and burns in the combustion chamber. Probably the earliest sign is that your oil level is low and you need to add oil between oil changes. You are using oil most likely because of cylinder wear. The other sign and it is hard to miss is smelly exhaust. Burning oil is distinctive and it emits a blue smoke out the exhaust pipe. Pay attention if you are using oil – you are probably burning it. (If it is not on the driveway).

Curious, often one or more cylinder in an engine experiences more wear than the others. It is not uncommon to see compression lower in one or 2 cylinders. I am told that is because the engine tends to stop with the pistons in the same place each time. For example the engine may stop most of the time with the #3 piston halfway in its up-stroke.

Why? Because the friction points of an engine are not perfectly balanced. The harmonics are unequal. One bearing or one ring will have more friction in its fit or surface so that when the engine winds down, it tends to stops at that spot. This is the nature of an engine as parts are manufactured within tolerances. They are not made to fit the exact pair that they will be matched with. During the first few hundred miles of driving, the engine is “broken in” as these parts made in different manufacturing shops are fit under use to each other. They are different and hence the difference in fit.

Taking this example further, that piston that stops half way in its upstroke loses the oil lubrication as it sits. The oil drains down to the crankcase. Therefore, when it is cranked over the next morning, it has a dry ring for the longest period – the half of the up stroke and the full down stroke before it picks up oil. In real operation, all of the oil does not drain away and the friction is not severe, but to the extent that this ring has a friction disadvantage, wear occurs there more dynamically. Do you now see how one cylinder will have more wear than the others?

When this happens, you can actually feel the weak cylinder with the imbalance of compression. In addition, the blowby is wasted energy, not focused on the top of the piston, but rather leaking by into the crankcase.

What can be done about Blowby?

Engine rebuild, overhaul or replacement are the options on the table. How much does that cost? For a car, between $2,000 and $8,000 depending on the engine and who you have do the work. For a Class VIII truck, between $7,000 and $25,000, again depending on what needs to be done and who is doing it.

BUT – there are some options to those big repair bills and just putting up with the problem and running the engine into the ground until it just dies.

Here is where things get interesting and this is what fascinated me so much that I joined the company that provides this option. CerTech makes a gel that when added to the oil creates a ceramic coating on the inside working surfaces of the engine. This new surface is sintered on – think of fire glazing, powder coating and tungsten carbide. Yes – tungsten carbide, the material that revolutionized the drill bit, saw blade and machine tool industries. They are all sintered into place.

Benefit of sintering is that the new surface gets down to nanoparticle, liquid state and embeds itself in to the pores of the metal surface. It is a permanent resurfacing. It will not flake or peel off.

Remember the engine harmonics above? CerTech Gels balance the harmonics of the engine. Can you imagine the power increase from a balanced engine?

The CerTech sintered surface is extremely hard – harder than tungsten carbide. And extremely strong too.

Is CerTech safe? In over 10 years of commercial use, thousands of car owners have gotten results and there has never been a claim of damage. Plus, CerTech is covered by a Product Liability Policy to cover any damage if it does happen.

Far from being an oil additive, CerTechGels actually resurfaces the metal.

Enough said.

I wrote this report not as a technical paper, but as an informative paper for the typical engine owner that is trying to figure out what is going on with their car, truck, or motor home or pump equipment. I have not credited anyone or any entity as most of what I have written is common knowledge and I have accumulated it from my experiences over many years. Take it for what it is worth and I hope you can obtain value from its contents.

Learn more at CerTechGels.

Bob Pond


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    • profile image


      6 years ago

      Ah, that is a question I had too. To the contrary - Lab studies and over 10 years successful use has proven the claim that material build up is controlled by friction and once optimized tolerances are attained, never an engine or device damaged. Never.

    • profile image


      6 years ago

      If it is an uncontrolled metal resurfacing agent, what is to prevent this product (and others like it) from building up and clogging the close tolarence oil passages located elsewhere in the engine? Seems to me (a 20+ year aircraft mechanic) that this product will cause more damage if used.... Overheated bearings, clogged / restricted oil return orifices, sludge & etc.

    • profile image


      6 years ago

      Motorcycles are a prefect application. Order 1 syringe of Gear and use 1/2 in beginning and then 1/2 about 100 miles later.

    • profile image


      6 years ago

      Will it work on a motorcycle?

    • profile image


      6 years ago

      Tom - A good conversion for the product (we replaced suppliers) is 45 mph. Make first application a few hours before oil change and the follow up after oil change and that will provide optimal benefit.

    • profile image


      6 years ago

      You might take a look at for more information about chemically resurfacing metal to metal friction surfaces. This is proven technology regardless of your prior experiences. The best way to find out is to prove it to yourself. If the turtle doesn't stick his head out, he never goes anywhere.

    • profile image


      6 years ago

      hi thank you for ur information but do you know how to measure the blow-by of unfired engine which is one cylinder without using pressure sensor because it's expensive.

      thank u

    • profile image

      srikanta das 

      7 years ago

      very usefull but if checking process of blowby is show oby animataion type then it quit more use full

    • Niknmax profile imageAUTHOR

      Bob Pond 

      8 years ago from Anaheim, CA

      Pete - The product lasts 65,000 miles, so for many it is a one time use. Nik

    • profile image

      t5 pete 

      8 years ago

      is this a one time use of will you have to use it every time you change the oil in our cars.

      Thankyou pete

    • profile image


      8 years ago

      Actually learned something new here. Thanks for the info.


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